1. Technical Field
The present invention relates to surface-emitting lasers, methods for manufacturing surface-emitting lasers, devices and electronic apparatuses.
2. Related Art
Semiconductor lasers include edge-emitting lasers that emit a laser light at an edge of a semiconductor substrate, and surface-emitting lasers that emit a laser light from a surface of a semiconductor substrate. Surface-emitting lasers are characterized in that the laser emission angle is isotropic and small compared to edge-emitting lasers. When a surface-emitting laser is used as a light source for optical communications, for example, a large optical output is required. In order to increase the output of a surface-emitting laser, an enlargement of its laser emission aperture is effective. However, when the laser emission aperture is enlarged, the laser emission angle becomes larger. When the laser emission angle becomes larger, and for example, when the surface-emitting laser and an optical fiber are directly, optically coupled without a lens or the like, the optical coupling efficiency is lowered, and their mounting margin is reduced.
According to a conventional method to compose a smaller laser emission angle of a surface-emitting laser, an upper surface of a columnar section composing a resonator of the surface-emitting laser is formed into a convex lens shape (lens layer or contact layer). An emitted light of the surface-emitting laser is converged by the lens layer or the contact layer, whereby the laser emission angle becomes smaller (for example, see FIG. 1, FIG. 7, and FIG. 8 of Japanese Laid-open Patent Application 2000-76682).
However, it should be noted that, in the actual surface-emitting laser, the lens layer also functions as a part of the resonator (an upper DBR: distributed reflection type multilayer mirror). By this, the index of reflection of the upper DBR considerably changes depending on the thickness of the lens layer. In particular, when the index of reflection in an area adjacent to the center axis of the columnar section composing the resonator lowers, demerits on basic characteristics such as the threshold value, slope efficiency and the like become greater than the merit of beam reshaping (convergence) by the lens layer. Sometimes, laser oscillation itself would not occur.
The present invention has been made in view of the above circumstances, and its object is to provide surface-emitting lasers in which highly accurate dimensions can be readily made at the center axis of a resonator, methods for manufacturing the surface-emitting lasers, devices and electronic apparatuses.
Also, it is an object of the present invention to provide surface-emitting lasers wherein a desired index of reflection can be excellently obtained at the center axis of a resonator, methods for manufacturing the surface-emitting lasers, devices and electronic apparatuses.
Moreover, it is an object of the present invention to provide surface-emitting lasers that can reduce the laser emission angle, methods for manufacturing the surface-emitting lasers, devices and electronic apparatuses.